Bear McCreary's site has a slew of video clips from Battlestar Galactica, showpiecing his compositions.
The "Passacaglia" clip is one of the emotionally most difficult parts of BSG for me to watch. Especially the Boomer parts of it. It is an amazingly powerful piece of work. It's like watching "Out of Gas". Painful, beautiful and an intensely rewarding experience. The music is a huge part of that.
If you have not seen all of BSG season 1 yet, I do not recommend watching those scenes, as they are definitely spoilerish.